The present invention relates to a chemical amplification type positive resist composition of usable in the fine processing in the production of semiconductor.
The fine processing in the production of semiconductor has usually been performed by adopting the lithography process using a resist composition. In the lithography process, principally, resolution can be improved by shortening wavelength for exposure, as indicated by the Rayleigh""s equation for limit of diffraction. Accordingly, the wavelength of the light source for a lithography process used in the production of semiconductors has become shorter and shorter in such order of a g-ray at a wavelength of 436 nm, an i-ray at a wavelength of 365 nm, and a KrF excimer laser at a wavelength of 248 nm. The ArP excimer laser at a wavelength of 193 nm is expected the next generation light source.
Since lenses in exposing machines using an ArF excimer laser have a shorter lifetime as compared with the lenses for the conventional exposing light source, a shorter time period for exposing such lenses to ArF excimer laser rays preferred. In order to make the exposure time shorter, the sensitivity of the resists is to be increased, and for such purpose, so called chemical amplification type resists are used. The-chemical amplification type resist contains a resin having a group cleavable by the action of an acid, and utilizes a catalytic action of the acid generated by exposure to the ray.
It has been known that resins used in resists to be exposed to ArF excimer lasers preferably have no aromatic ring in order to insure the transmittance of the resists and have an alicyclic ring in place of an aromatic ring in order to confer a dry etching resistance. Various resins have been known as resins meeting such requirements. For example, D. C. Hofer, J. Photopolym. Sci. Technol., Vol. 9, No. 3, pages 387-398 (1996) describes much resins. The known resins, however, have a problem that peeling on development is liable to occur due to insufficient adherence during development, particularly when the polarity is not sufficient.
S. Takechi et al., J. Photopolym. Sci. Technol., Vol. 9, No. 3, pages 475-487 (1996) and JP-A-9-73173 describe that, when polymers or copolymers of 2-methyl-2-adamantyl methacrylate are used as resins for a chemical amplification type resist, a positive working action is realized by cleavage of the 2-methyl-2-adamantyl group by the action of an acid and a high dry etching resistance, high resolution and a good adherence to substrate are obtained. JP-A-10-274852 describes that the adherence to substrate is improved by using a resin having a butyrolactone residue in a part of the polymerization units, as a resin composing a chemical amplification type positive resist composition. In addition, JP-A-10-319595 describes a positive resist composition using a resin having a carboxyl group protected by a xcex3-butyrolactone-3-yl residue.
On the other hand, since the chemical amplification type resists utilizes the action of an acid, the profiles are liable to be bottom-tailed by deactivation of the acid when the substrate is of a basic nature. It is known that this problem can be resolved by adding a large amount of a basic quencher substance. Addition of a large amount of such quencher substance, however, results in decrease of the sensitivity. When a ArF eximer laser is used as the light for exposure, the resist is often applied on a substrate having a low reflection, such as an organic or inorganic anti-reflection film. When such a substrate having a low reflection is used, the profile of the resist is generally deteriorated to a taper shape, although dimension uniformity is effectively improved. Therefore, chemical amplification type resists have a problem in that performances, particularly the profile, are varied depending on the kind of the substrate.
The object of the present invention is to provide a chemical amplification type positive resist composition, which contains a resin component and an acid generator; is suitable to use in a lithography process using ArF excimer laser, KrF excimer laser or the like; is superior in various resist performances such as sensitivity, resolution, adherence to substrate and so on; has a low substrate-dependency even when it is applied to a basic substrate or a low reflection substrate; and confer a good profile on every substrate.
The co-pending application Japanese Patent Application No. 11-238542, filed by the present applicant, describes that a resin having an adamantine polymerization unit with a specific chemical structure and a of polymerization unit with a high polarity is effective in improving adherence to substrate. The present inventors have carried out further studies on systems using the resin having a butyrolactone residue disclosed in JP-A-10-274852 and JP-A-10-319595 and the resin having an adamantine polymerization unit disclosed in a Japanese Patent Application No. 11-238542 in chemical amplification type positive resist composition. As the result, they have found that, in these compositions, the resolution is improved and profiles on a basic substrate or a low reflection substrate are also improved by using an acid generator having a specific chemical structure. Thus, the present invention has been completed.
The present invention provides a positive resist composition which comprises
a resin having 2-alkyl-2-adamantyl (meth)acrylate polymerization unit represented by the following formula (I): 
wherein R1 represents hydrogen or methyl and R2 represents an alkyl, and being insoluble or barely soluble in alkali, but being converted to soluble in alkali by the action of an acid;
and an acid generator represented by the following formula (V): 
wherein Q1, Q2 and Q3 independently represent hydrogen, a hydroxyl group, an alkyl having 1 to 6 carbon atoms or an alkoxy having 1 to 6 carbon atoms, and n is an integer of 4 to 8.
The polymerization unit 2-alkyl-2-adamantyl (meth)acrylate represented by the formula (I) described above is a unit formed by opening the double bond of (meth)acrylic acid portion in the 2-alkyl-2-adamantyl acrylate or 2-alkyl-2-adamantyl methacrylate. The resin as a component of the resist composition of the present invention may be a polymer having 2-alkyl-2-adamantyl (meth)acrylate polymerization unit alone, but, it is preferably a copolymer having one or more of other polymerization units together with the above unit.
Examples of the polymerization unit, other than 2-alkyl-2-adamantyl (meth)acrylate, preferably used to form a copolymer include
3-hydroxy-1-adamantyl (meth)acrylate polymerization unit represented by the following formula (II): 
wherein R3 represents hydrogen or methyl;
xcex1-(meth)acryloyloxy-xcex3-butyrolactone polymerization unit represented by the following formula (III): 
wherein R4 represents hydrogen or methyl, and R5, R6 and R7 independently represent hydrogen or an alkyl; and
xcex2-(meth)acryloyloxy-xcex3-butyrolactone polymerization unit represented by the following formula (IV): 
wherein R4, R5, R6 and R7 are as defined above.
The polymerization Unit 3-hydroxy-1-adamantyl (meth)acrylate represented by the formula (II) can be formed by opening the double bond of (meth)acrylic acid portion in 3-hydroxy-1-adamantyl (meth)acrylate. The polymerization unit xcex1-(meth)acryloyloxy-xcex3-butyrolactone represented by the formula (III) can be formed by opening the double bond of (meth)acrylic acid portion in xcex1-(meth)acryloyloxy-xcex3-butyrolactone which may be substituted with an alkyl in the lactone ring. The polymerization unit xcex2-(meth)acryloyloxy-xcex3-butyrolactone represented by the formula (IV) can be formed by opening the double bond of (meth)acrylic acid portion in xcex2-(meth)acryloyloxy-xcex3-butyrolactone which may be substituted with an alkyl in the lactone ring.
The resin as a component of the resist composition of the present invention has 2-alkyl-2-adamantyl (meth)acrylate polymerization unit represented by the formula (I). In addition to this polymerization unit, the resin may optionally have 3-hydroxy-1-adamantyl (meth)acrylate polymerization unit represented by the formula (II) and/or xcex1-(meth)acryloyloxy-xcex3-butyrolactone polymerization unit represented by the formula (III), or xcex2-(meth)acryloyloxy-xcex3-butyrolactone polymerization unit represented by the formula (IV). Therefore, the resin can be produced by polymerization or copolymerization of 2-alkyl-2-adamantyl (meth)acrylate monomer optionally with the above described other monomers. When 3-hydroxy-1-adamantyl (meth)acrylate is used as one of the copolymerization components, a copolymer having a unit of the formula (II) in addition to the unit of the formula (I) is obtained. When an xcex1-(meth)acryloyloxy-xcex3-butyrolactone in which the lactone ring may be substituted with alkyl is used as one of the copolymerization components, a copolymer having a unit of the formula (III) in addition to the unit of the formula (I) is obtained. When an xcex2-(meth)acryloyloxy-y-butyrolactone in which the lactone ring may be substituted with alkyl is used as one of the copolymerization components, a copolymer having a unit of the formula (IV) in addition to the unit of the formula (I) is obtained. Furthermore, when both of these 3-hydroxy-1-adamantyl (meth)acrylate and xcex1-(meth)acryloyloxy-xcex3-butyrolactone are used, a terpolymer having units of the formulae (I), (II) and (III) is obtained. As described later further monomers may be used in the copolymerization.
2-Alkyl-2-adamantyl (meth)acrylates can be produced by the reaction of a 2-alkyl-2-adamantanol or a metal salt thereof with an acryloyl halide or a methacryloyl halide. 3-Hydroxy-1-adamantyl (meth)acrylate is commercially available. It can also be produced by hydrolyzing 1,3-dibromoadamantane to give 1,3-dihydroxyadamantane, followed by reacting the resulting product with acrylic acid, methacrylic acid or a halide thereof. The xcex1- or xcex2-(meth)acryloyloxy-y-butyrolactones can be produced by reacting acrylic acid or methacrylic acid with xcex1- or xcex2-bromo-xcex3-butyrolactone in which the lactone ring may be substituted with alkyl, or by reacting an acryloyl halide or methacryloyl halide with xcex1- or xcex2-bromo-xcex3-butyrolactone in which the lactone ring may be substituted with alkyl.
The polymerization unit 2-alkyl-2-adamantyl (meth)acrylate represented by the formula (I) contributes to the transmittance of the resist and improvement of dry etching resistance due to the presence of the adamantane nucleus which is an alicyclic ring. Since the 2-alkyl-2-adamantyl group in this unit is cleaved by the action of an acid, the unit contributes to enhance solubility in alkali after exposure of the resist film. The group R2 in the formula (I) is an alkyl group. This alkyl usually have about 1 to 8 carbon atoms. Preferably, it is a linear chain in usual case but may be branched when it has 3 or more carbon atoms. Examples of R2 include methyl, ethyl, propyl, isopropyl and butyl. Amongst them, methyl or ethyl, particularly ethyl, is preferred as R2 for improvement of adhesiveness to substrate or resolution.
Examples of monomers used for introducing the 2-alkyl-2-adamantyl (meth)acrylate polymerization unit represented by the formula (I) in the resin include 2-methyl-2-adamnatyl acrylate, 2-ethyl-2-adamnatyl acrylate, 2-methyl-2-adamnatyl methacrylate and 2-ethyl-2-adamnatyl methacrylate. Among them, 2-methyl-2-adamnatyl methacrylate and 2-ethyl-2-adamantyl methacrylate are preferred.
Both the polymerization unit 3-hydroxy-1-adamantyl (meth)acrylate represented by the formula (II), the polymerization unit xcex1-(meth)acryloyloxy-xcex3-butyrolactone represented by the formula (III) and the polymerization unit xcex2-(meth)acryloyloxy-xcex3-butyrolactone represented by the formula (IV) have higher polarity and contribute to improvement of adherence of the resist to the substrate. In addition, these polymerization units contribute resolution of the resist. The polymerization unit 3-hydroxy-1-adamantyl (meth)acrylate contributes to improvement of dry etching resistance of the resist. Furthermore, the polymerization unit xcex2-(meth)acryloyloxy-xcex3-butyrolactone contribute to improvement of transmission of the resist.
For introducing the 3-hydroxy-1-adamantyl (meth)acrylate polymerization unit represented by the formula (II) in the resin, 3-hydroxy-1-adamnatyl acrylate or 3-hydroxy-1-adamnatyl methacrylate is used in producing the resin. In the formula (III), R5, R6 and R7, which are same to or different from each other, represent hydrogen or an alkyl. This alkyl can have about 1 to 6 carbon atoms and may be a linear chain or a branched chain when it has 3 or more carbon atoms. Specific examples of alkyl as R5, R6 and R7include methyl, ethyl, propyl and butyl. Examples of the monomer used for introducing the xcex1-(meth)acryloyloxy-xcex3-butyrolactone polymerization unit represented by the formula (III) in the resin include xcex1-acryloyloxy-xcex3-butyrolactone, xcex1-methacryloyloxy-xcex3-butyrolactone, xcex1-acryloyloxy-xcex2,xcex2-dimethyl-xcex3-butyrolactone, xcex1-methacryloyloxy-xcex2,xcex2-dimethyl-xcex3-butyrolactone, xcex1-acryloyloxy-xcex1-methyl-xcex3-butyrolactone and xcex1-methacryloyloxy-xcex1-methyl-xcex3-butyrolactone. Examples of the monomer used for introducing the xcex2-(meth)acryloyloxy-xcex3-butyrolactone polymerization unit represented by the formula (IV) in the resin include xcex2-acryloyloxy-xcex3 and xcex2-methacryloyloxy-xcex1-methyl-xcex3-butyrolactone.
The resins used in chemical amplification type positive resist are generally insoluble or barely soluble in alkali before the exposure to light in the lithography process. It become soluble in alkali after cleavage of apart of groups by the action of an acid. In the resin used in the present invention, the 2-alkyl-2-adamantyl group in the formula (I) is cleaved by the action of an acid. If necessary, the resin may further contain other polymerization units having a group cleavable by the action of an acid.
Examples of such group include alkyl esters such as methyl ester and tert-butyl-ester, acetal type esters such as methoxymethyl ester, ethoxymethyl ester, 1-ethoxyethyl ester, 1-isobutoxyethyl ester, 1-isopropoxyethyl ester, 1-ethoxypropyl ester, 1-(2-methoxyethoxy)ethyl ester, 1-(2-acetoxyethoxy)ethyl ester, 1-[2-(1-adamantyloxy)ethoxy]ethyl ester, 1-[2-(1-adamantylcarbonyloxy)ethoxy]ethyl ester, tetrahydro-2-furyl ester and tetrahydro-2-pyranyl ester, and alicyclic ester such as isobornyl ester. Monomers used for introducing these polymerization units having a carboxylate ester in the resin may be acrylic monomer such as methacrylic ester and acrylic ester or alicyclic monomers having a carboxylic eater bound thereto such as norbornenecarboxylic ester, tricyclodecenecarboxylic ester and tetracyclodecenecarboxylic ester.
The resin used in the present invention preferably contains the polymerization unit having a group cleavable by the action of an acid in a range of 30 to 80% by mole based on the total polymerization unit in the resin, although the preferred range varies depending on the kind of irradiation rays used in the exposure for patterning and the kind of group cleavable by the action of an acid. In addition, it is preferred that the polymerization unit 2-alkyl-2-adamantyl (meth)acrylate represented by the formula (I) is present in an amount of 20% or more based on the total polymerization unit in the resin. It is preferred that the polymerization unit 3-hydroxy-1-adamantyl (meth)acrylate represented by the formula (II) and/or the polymerization unit xcex1-(meth)acryloyloxy-xcex3-butyrolactone represented by the formula (III) are present in a total amount of 20 to 70% by mole based on the total polymerization unit in the resin, when the resin has the polymerization unit represented by the formula (II) and/or the polymerization unit represented by the formula (III). Furthermore, it is preferred that the polymerization unit xcex2-(meth)acryloyloxy-xcex3-butyrolactone represented by the formula (IV) is present in an amount of 20 to 70% by mole based on the total polymerization unit, when the resin has the polymerization unit represented by the formula (IV).
It is preferred, therefore, to conduct a copolymerization using a monomer mixture containing 20 to 80% by mole, preferably 30 to 80% by mole, of 2-alkyl-2-adamantyl (meth)acrylate for introducing the unit of the formula (I) in the resin, and 20 to70% by mole in total of 3-hydroxy-1-adamantyl (meth)acrylate for introducing the unit of the formula (II) and/or xcex1-(meth)acryloyloxy-xcex3-butyrolactone, which may be substituted with alkyl in the lactone ring, for introducing the unit of the formula (III), when the resin has the polymerization unit represented by the formula (II) and/or the polymerization unit represented by the formula (III).
It is preferred, therefore, to conduct a copolymerization using a monomer mixture containing 20 to 80% by mole, preferably 30 to 80% by mole, of 2-alkyl-2-adamantyl (meth)acrylate for introducing the unit of the formula (I) in the resin, and 20 to 70% by mole of xcex2-(meth)acryloyloxy-xcex3-butyrolactone, which may be substituted with alkyl in the lactone ring, for introducing the unit of the formula (IV), when the resin has the polymerization unit represented by the formula (IV).
The resin having the polymerization unit of the formula (I) and optionally the polymerization unit(s) of the formula (II) and/or the formula (III) or the formula (IV) may also contain another polymerization unit having a group cleavable by the action of an acid, as described above. The resin may further contain another polymerization unit having a group which is not cleavable by the action of an acid insofar as it is within a range that the effect of the invention is not adversely affected. Examples of the other polymerization unit optionally contained include polymerization units having a free carboxylic acid group, polymerization unit introduced from maleic anhydride, polymerization unit introduced from itaconic anhydride and polymerization unit introduced from (meth)acrylonitrile.
The acid generator as the other component of the resist decomposes to generate an acid upon the action of radiation rays such as a light and electric rays on the substance itself or on a resist composition containing the substance. The acid generated from the acid generator acts on the resin and the group cleavable by the action of an acid is cleaved by the action of the acid. In the present invention, a sulfonium salt compound represented by the formula (V) described above is used as the acid generator.
In the formula (V), Q1, Q2 and Q3, which are same to or different from each other, represent hydrogen, a hydroxyl group, an alkyl having 1 to 6 carbon atoms or an alkoxy having 1 to 6 carbon atoms. The alkyl as well as alkoxy may be a linear chain or a branched chain when they have 3 or more carbon atoms. Examples of the alkyl include methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, pentyl and hexyl. Examples of alkoxy include methoxy, ethoxy, propoxy, butoxy and the like.
In addition, in the formula (V), n is an integer of 4 to 8 representing the number of carbon in the fluoroalkane portion of perfluoroalkanesulfonate ion which is an anion. One of the characteristics of the present invention resides in that a sulfonium salt having a perfluoroalkanesulfonate anion having a number of carbon atoms is used as an acid generator. By using such a compound as the acid generator, the resolution of the resist is improved and its profile on a basic substrate or a low reflection substrate is also improved.
The sulfonium salt represented by the formula (V) may be a commercial product if available or may be produced according to the conventional process. For example, it can be produced by reacting a corresponding triphenylsulfonium bromide with a silver perfluoroalkanesulfonate; by reacting a corresponding diphenylsulfoxide, a benzene compound and a perfluoroalkanesulfonic acid in the presence of trifluoroacetic anhydride according to the description in Chem. Pharm. Bull., Vol. 29, page 3753 (1981); or by reacting a corresponding aryl Grignard""s reagent with thionyl chloride, then with triorganosilyl halide to give a triarylsulfonium halide, which is reacted with a silver perfluoroalkanesulfonate according to the description in JP-A-8-311018. In addition, compounds of the formula (V) in which Q1, Q2 or Q3 represent a hydroxyl group can be produced by treating a triphenylsulfonium salt having a tert-butoxy group on the benzene ring with a sulfonic acid to eliminate the tert-butyl group according to the description in JP-A-8-311018.
Specific examples of the sulfonium salt corresponding to the formula (V) include the following compounds:
triphenylsulfonium perfluorobutanesulfonate, triphenylsulfonium perfluorooctanesulfonate, 4-methylphenyldiphenylsulfonium perfluorobutanesulfonate, 4-methylphenyldiphenylsulfonium perfluorooctanesulfonate, 4-hydroxyphenyldiphenylsulfonium perfluorobutanesulfonate, 4-hydroxyphenyldiphenylsulfonium perfluorooctanesulfonate, 4-methoxyphenyldiphenylsulfonium perfluorobutanesulfonate, 4-methoxyphenyldiphenylsulfonium perfluorooctanesulfonate, tris(4-methylphenyl)sulfonium perfluorobutanesulfonate, trim(4-methylphenyl)sulfonium perfluorooctanesulfonate, tris(4-methoxyphenyl)sulfonium perfluorobutanesulfonate, and tris(4-methoxyphenyl)sulfonium perfluorooctanesulfonate.
The resist composition of the invention is a combination of a resin having A 2-alkyl-2-adamantyl (meth)acrylate polymerization unit represented by the formula (I) with a sulfonium salt having a perfluoroalkanesulfonate anion containing a number of carbon atoms represented by the formula (V) described above as an acid generator. If desired, other acid generators can be co-used in addition to the sulfonium salt. Examples of other acid generators include sulfonium salts other than that represented by the formula (V), other onium salts such as iodonium salts, organic halogene compounds such as haloalkyltriazine compounds, sulfone compounds such as disulfones and diazomethanedisulfones acid, various sulfonic acid esters and the like.
It has been known that, generally, in the composition of chemical amplification type positive resist, deterioration of performance due to deactivation of an acid by standing after exposure can be improved by adding a basic compound, particularly a basic nitrogen-containing organic compound such as an amine compound, as a quencher. Likewise, in the present invention, addition of such a basic compound is preferred. Specific examples of the basic compounds used as quenchers include the compounds represented by the following formulae: 
wherein R11, R12, R13, R14, and R15 independently represent hydrogen, alkyl which may be substituted with a hydroxyl group, cycloalkyl, aryl or alkoxy, and A represents alkylene, carbonyl or imino. The alkyl and alkoxy represented by R11, R12, R13, R14 and R15 usually have about 1 to 6 carbon atoms, cycloalkyl usually have about 5 to 10 carbon atoms and aryl usually have about 6 to 10 carbon atoms. The alkylene represented by A usually have 1 to 6 carbon atoms and may be a linear chain or a branched chain.
The resist composition of the invention preferably comprises the resin in a range of about 80 to 99.9% by weight and the acid generator in a range of about 0.1 to 20% by weight, based on the total solid content. When a basic compound as a quencher is used, preferably it is contained in a range of about 0.01 to 1% by weight, based on the total solid content. In addition, the resist composition of the present invention may contain, if necessary, various additives such as photo-sensitizer, dissolution inhibitor, other resin, surfactant, stabilizer and dye.
The resist composition of the invention is usually used as a resist solution in which the above described components are dissolved in a solvent and the resist solution applied onto a substrate such as a silicone wafer. The solvent usable here may be anyone insofar as it dissolve the components, has a suitable drying rate and gives a uniform and smooth film after evaporation of the solvent. Solvent generally used in this field can be used. Examples of the solvent include glycol ether esters such as ethyl cellosolve acetate, methyl cellosolve acetate and propylene glycol monomethyl ether acetate; esters such as ethyl lactate, butyl acetate, amyl acetate and ethyl pyruvate ketones such as acetone, methyl isobutyl ketone, 2-heptanone and cyclohexanone; and cyclic esters such as xcex3-butyrolactone. One of these solvents can be used singly or two or more of the solvents can be used in combination.
The resist film formed by applying the resist solution on a substrate and drying is subjected to exposure treatment for patterning, then to heat treatment for promoting protective group-eliminating reaction and finally developed with an alkaline developer. The alkaline developer used here may be any aqueous alkaline solution used in this field. An aqueous solution of tetramethyl ammonium hydroxide or (2-hydroxyethyl)trimethyl ammonium hydroxide (common name: choline) is generally used as a developer.